In recent years, liquid crystal display (LCD) panels having characteristics of lightweight and high definition have been widely used in various equipment including cellular phones. The LCD panels are traditionally manufactured as follows. A heat-curable sealing agent composition based on an epoxy resin is applied to an LCD glass substrate, followed by precuring. Subsequently, a counter substrate is superposed thereon and bonded together by heating and pressing, so that an LC sealing cell is fabricated. A liquid crystal is then injected in vacuum and thereafter the LC inlet is sealed.
The above LCD panel manufacturing process, however, tends to result in cell gap variations attributed to thermal stress by heat curing. Further, the LC injection is a time-consuming step. Accordingly, it has been difficult to reduce the manufacturing process time and to improve productivity of high-definition small and large LCD panels.
To solve these problems use of such LC sealing agents have been proposed as light-curable acrylic LC sealing agents based on acrylate or methacrylate, light-curable epoxy LC sealing agents, and light and heat-curable LC sealing agents based on partially acrylated or partially methacrylated bisphenol epoxy resins.
Of these sealing agents, the light and heat-curable LC sealing agents are proposed for use in processes of manufacturing LCD panels, specifically as follows. The sealing agent is applied in vacuum on a substrate on which an electrode pattern and an alignment layer have been provided. Subsequently, a liquid crystal is dropped on the sealing agent-coated substrate or a counter substrate, and the substrates are laminated together. Thereafter, first-stage light curing is performed by UV irradiation or the like to quickly fix the substrates, namely, to form a cell gap. Further, second-stage heat curing is carried out without use of a pressing jig to cure completely the sealing agent. For example, such process is disclosed as one drop fill in JP-A-H09-5759.
Gap formation by light curing is one of the characteristics required for the LC sealing agent compositions used in the one drop fill. When the first-stage light curing results in inadequate gap formation, the opposed substrates may be misaligned or the heat-curing component (for example, epoxy resin) that has not been cured may exude in the subsequent second-stage heat curing step, leading to contamination of liquid crystal. Particularly, the latter has been perceived as a problem in view of critical influence on LCD panel performance. Moreover, improvement has been desired for curing properties in area shaded by the wiring.
JP-A-2001-133794 discloses an LC sealing agent composition for one drop fill that contains a light-curable component, a heat-curable component and a light curing agent, and that achieves specified decrease in LC specific resistance and specified change in LC phase transition point. However, there is no disclosure that describes the composition's gap formation properties by light curing and curing properties in area shaded by the wiring. Thus, reliability of the LCD panels obtained is not always satisfactory.
Moreover, the LC sealing agent compositions are required for other properties, such as bonding reliability in long-term exposure to high temperature and high humidity, retention of LC electro-optic properties, and no influence on the LC alignment.
It is therefore an object of the present invention to provide a liquid crystal sealing agent composition that is favorably employable in the one drop fill, is excellent in curing properties in the first-stage light curing to give a satisfactory cured product, and has superior curing properties in area shaded by the wiring. Specifically, the object is to provide a one-component light and heat-curable liquid crystal sealing agent composition that is excellent in cell gap stability exhibited after formation of a cell gap by light curing, permits prevention of contamination of the liquid crystal in the second-stage heat curing, and has superior bonding reliability. It is another object of the invention to provide a method for manufacturing a liquid crystal display panel by the one drop fill using the liquid crystal sealing agent composition, and a liquid crystal display panel.